1. Field of the Invention
This invention relates to a tubular shaft, particularly for ship propulsion, comprising a torque-transmitting tubular structure that comprises at least one torque-transmitting shell having an elasticity extending along a helical line.
2. Description of the Prior Art
Propulsion systems in which periodic torsional vibration occurs, e.g., all drives that comprise piston engines, must be provided with special compensating and damping means in order to avoid overloads due to resonance and to ensure a satisfactory operation and the required useful life. Extreme conditions will particularly arise in ship propulsion systems, which comprise very powerful two-stroke-cycle engines and long drive shafts and require highly expensive and relatively large vibration dampers. By that vibration damping the resonance peaks can be decreased below the loads which are permissible for the materials employed, particularly in the shafts, and the stiffness of the materials may be reduced to shift the resonance peaks toward lower speeds. To that end it is already known to incorporate an intermediate shaft made of fiber-reinforced plastic material in the shafting of ship propulsion systems so that the shafting is made softer and lighter in weight. The shafts made of fiber-reinforced plastic material must be tubular shafts and may consist of one or more torque-transmitting shells. The reinforcing fibers extend along helical lines and cross each other or their sense of twist changes from shell to shell so that torsional stresses can uniformly be taken up. The fibers are embedded in a synthetic resin and this results in a certain damping property but that damping property remains very small and virtually cannot be influenced. For this reason such a tubular shaft made of fiber-reinforced plastic material cannot be used as an effective damping element within a drive shafting.